Moisture curable polyurethane systems

ABSTRACT

The disclosed process for making a high % solids, one-part, moisture-curable, essentially flowable or pumpable, high equivalent weight polyurethane (i.e. polyol-polyisocyanate adduct) prepolymer composition involves de-watering the polyol component of the reaction mixture with an alkaline earth metal oxide, preferably calcium oxide; adding the minimum acceptable level of catalyst for the NCO/polyol reaction; exothermically reacting a partially hindered aliphatic polyisocyanate such as isophorone diisocyanate (IPDI) and a partially hindered aromatic polyisocyanate such as 2,4-tolylene diisocyanate seriatim, so that at least about one-fourth of the IPDI reacts before the 2,4TDI is added; and then adding more catalyst for the moisture cure. Careful control over the amounts and selection of raw materials, proper selection of sequences of addition of these amounts and materials, careful de-watering of the reaction mixture and proper adjustment or selection of isocyanate functionality minimizes random and undesired reactions and side reactions (e.g. chain extension) during prepolymer formation and insures good elastomeric properties in the ultimately cured product. As a result, this well-controlled prepolymer composition can be made efficiently with simple mixing equipment. One of the preferred coating or sealant uses for the prepolymer product is cured elastomeric coatings for the building industry, e.g. as a primary seal in roofing.

United States Patent 1 1 Coyner et al.

1 MOISTURE CURABLE POLYURETHANE SYSTEMS [751 Inventors: Robert N.Coyner, Hopkins; Peter Skujins, Minneapolis, both of Minn.

260/25 AT; 260/37 N; 260/775 MA; 260/775 TB [51] Int. Cl. C08G 18/02;C086 18/12 [58] Field 01' Search 260/775 AA, 77.5 AT, 33.6 UB

[56] References Cited UNITED STATES PATENTS 1830,03! 4/1958 Carterloll/77.5 1191186 6/1965 Mliller et a1. 360/775 3.351.573 11/1967Skreckoski l l v l c 2611/18 3.352.830 11/1967 Schmitt et al..l. H260/775 1425.973 2/1969 Shaw r l i A r i i l H 260/18 3.463.748 8/1969Scheibelhoffer Y l 4 260/18 TN 3.479335 11/1969 Blomeyer et 11....260/775 AA 3.549.569 12/1970 Farah et a1 l l l l 117/127 3.554.9631/1971 Fischer 1. 260/453 3.651508 3/1972 Segur et a1. 260/775 AA3.663.514 5/1972 Campbell et a1 .1 160/775 OTHER PUBLICATIONSVeba-Chemie A.G. Diisocyanatesf Bulletin No. 22-E47l-l-4.

Primary E\'uminerM. J. Welsh Attorney. Agent, or Firm-Thomas M.Meshbesher 1 Nov. 11, 1975 1571 ABSTRACT The disclosed process formaking a high 7 solids onepart. moisturecurable. essentially flowable orpumpable. high equivalent weight polyurethane (ie polyolpolyisocyanateadduct) prepolymer composition involves de-watering the polyol componentof the reaction mixture with an alkaline earth metal oxide. preferablycalcium oxide: adding the minimum acceptable level of catalyst for theNCO/polyol reaction; exothermically reacting a partially hinderedaliphatic polyisocyanate such as isophorone diisocyanate (lPDl) and apartially hindered aromatic polyisocyanate such as 2.4tolylenediisocyanate seriatim. so that at least about one-fourth of the [PD]reacts before the 2.4 TDl is added; and then adding more catalyst forthe moisture cure Careful control over the amounts and selection of rawmaterials proper selection of sequences of addition of these amounts andmaterials. careful dewvatering of the reaction mixture and properadjustment or selection of isocyanate functionality minimizes random andundesired reactions and side reactions teig. chain extension) duringprepolymer formation and insures good elastomeric properties in theultimately cured product. As a result. this \\'ellcontrolled prepolymercomposition can be made efficiently with simple mixing equipment One ofthe preferred coating or sealant uses for the prepolymcr product iscured elastomeric coatings for the building industry. eg as a primaryseal in roofing 15 Claims. N0 Drawings MOISTURE CURABLE POLYURETHANESYSTEMS FIELD OF THE INVENTION This invention relates to one-part,moisture curable polyetherurethane prepolymer compositions, methods formaking them, methods for using them, and moisture cured elastomericcoatings derived from them. An aspect of this invention relates to aone-part moisture curable polyurethane system which is particularlyuseful in the construction industry, e.g. for providing a reasonablythick, water resistant, flexible coating on roof decks. Still anotheraspect of this invention relates to a method for making an elastomerforming, moisturecurable, one-part polyetherurethane prepolymer systemwhich is at least 90 or 95% by weight solids and which is made from apolyol and a combination of aliphatic and aromatic polyisocyanates atnormal ambient temperatures using relatively simple equipment. Stillanother aspect of this invention relates to a polyurethane prepolymersystem of the type described previously which is an anhydrous, pourable,viscosity-stable liquid at room temperature, which is adequatelyprotected from contamination by atmospheric moisture prior to cure, andwhich cures to an essentially colorstable elastomer.

DESCRIPTION OF THE PRIOR ART The art of one-part, elastomer-forming,moisturecurable polyurethane prepolymers has grown enormously in thepast several years and is now almost too vast to describe in detailwithout a lengthy treatise. The advantages and disadvantages of thesesystems are well known; nevertheless, a considerable amount of thepotential for these systems has not yet been fully realized. Forexample, the roof decks of residential and industrial buildings arestill generally covered with the timehonored, conventional laminarroofing materials. These materials are inexpensive and generally quiteadequate, but they lack the high-elongation properties of an elastomer.Theoretically, an elastomer-coated roof deck (and other uses in theconstruction industry of elastomeric coatings) could have a number ofoutstanding advantages (e.g. weatherability, flexibility, waterresistence, and ease of application) over conventional materials, andbutyl rubber has already been suggested for use as a primary seal forroof decks and as a top coat for existing roofs. To realize theseadvantages, it is important to be able to manufacture theelastomerforming material as efficiently and simply as possible, so thatcompetition with the existing materials can become commerciallypractical.

Polyurethane prepolymers can be made with relatively simple equipment(e.g. on a laboratory scale) or large, complex installations equippedwith sophisticated equipment such as solvent recovery systems, anotropicdistillation systems, volatile isocyanate strippers, heated mixers, andthe like. The use of simple equipment which does not depend on thesesophisticated devices or systems is desirable for several reasons.

To obviate the need for the sophisticated features of the large, complexinstallations and to provide a relatively simple prepolymermanufacturing process, it is necessary to confront a whole series ofproblems almost all at once. First, liquid water or water vapor is aserious contaminant during virtually all stages of production of theprepolymer product. Water as a contaminate can enter into the processfrom several sources, including ambient moisture (atmospheric watervapor etc.), residual water and water of hydration in raw materials suchas polyols, inorganic pigments or fillers, and the like. Azeotropicdistillation is commonly used to remove water from polyols but isenergy-consuming and can involve expensive equipment. A variety ofdesiccants are known to be effective in removing water from reactionmixtures; however, some desiccants remove the water by a reversiblemechanism which provides a latent future source of moisture and otherscan undesirably alter the chemical characteristics of the resultingproduct or the reaction conditions used to make it. Furthermore, it maystill be necessary to protect the desiccated product with inert, drygases or the like until it is packaged in moisture-proof containers.

Second, the isocyanate/active-hydrogen (e.g. NCO- IOH) reaction can berather poorly controlled, at least from a theoretical standpoint. Evenassuming that side reactions with moisture or other contaminants can beeliminated, the product of the reaction is often times only astatistical average of a wide range of possibilities. For example, thereaction between six equivalents of isocyanate and one mole of triolproduces, on the average, a tri-isocyanate. Nevertheless, the polyol mayhave reacted with the NCO at 0, l, 2, or 3 of its reactive sites,leaving some unreacted isocyanate, which balances out the NCO/OH ratiostatistically but does not add to the amount of useful prepolymer.Various combinations of heat, catalysts, prepolymer-forming rawmaterials, and incremental addition techniques (e.g. adding the catalystin two increments) have been used to improve the prepolymer-formingreactions and reduce the expense of wasted reactants (e.g. unreactedpolyisocyanate). However, the use of heat is not desirable if the goalis manufacturing the prepolymer with simple mixing equipment. Therelatively slow reaction between polyisocyanates and polyols(particularly those containing secondary hydroxyl groups) can be speededup significantly with catalysts. However, most catalysts speed upvirtually all NCO/active-hydrogen reactions in both directions and mayeven increase the possibility of random results.

Further difficulties result from the fact that the onepartmoisture-curable system may have to be custom made for a particular useand a particular set of elastomeric properties such as ultimate tensilestrength, modulus at elongation, elongation at break, moistureresistance, color-stability (e.g. resistance to yellowing), cellstructure (if a foamed elastomer is desired), and the like. Furthermore,it is often necessary to maintain the viscosity of the prepolymer systemwithin very narrow limits prior to cure. If a high elongation withadequate tensile strength is desired, it may be necessary or desirableto use a high equivalent weight polyol to make the prepolymer. In thisevent, the viscosity of the resulting prepolymer can be extremelysensitive to minor amounts of active-hydrogen-containing contaminants.

It is known that aliphatic polyisocyanates and combinations of aliphaticand aromatic polyisocyanates (as opposed to l00% aromaticpolyisocyanate-capped prepolymers) contribute to light stability,particularly ultraviolet stability, in the cured urethane polymer. It isalso known that, in some polyisocyanates, the NCO radicals differ intheir reactivity with polyols, and that this phenomenon can sometimes beutilized to reduce randomness in the prepolymer-forming reactions.However. any time a prepolymer-forming system is formulated with regardto one set of considerations (such as uv stability), some other set ofconsiderations (such as the desired properties of the cured polymer, thespeed of cure, the depth of cure in a film, etc.) may be compromised.This is why the urethane chemist must confront virtually all theproblems at the same time, and no overall solution can be arrived atthrough a single, straightforward manipulation of the raw materials orreaction conditions.

Accordingly, this invention does seek to confront all these problemswithout resorting to sophisticated equipment or complex techniques whichwould make competition with existing non-urethane materials impractical.

SUMMARY OF THE INVENTION Briefly, this invention involves: (l) utilizingan alkaline earth metal oxide (preferably calcium oxide) as a desiccantfor the polyoxyalkylene polyol component of the prepolymer-formingsystem and for the resulting reaction mixture and the prepolymerproduct; (2) using the minimum amount of catalyst (e.g. one of theconventional organo-tin compounds) to make the prepolymer, whereby themajor amount of catalyst for the moisture curing action is added afterthe prepolymer is formed; (3) exothermically reacting. without theaddition of heat, and aliphatic and aromatic polyisocyanate with thedesiccated polyol, whereby both types of polyisocyanate arecharacterized by NCO radicals of unequal reactivity and the aromaticisocyanate is preferably not added to the reaction mixture until atleast 25% of the number of equivalents of aliphatic isocyanate havereacted with the polyol; and (4) providing a functionality for theresulting prepolymer product which is greater than 2.0 but less than3.0, an NCO equivalent weight in excess of 1,000, and preferably highsolids, without increasing the viscosity so as to interfere with pumpingor casting at normal ambient temperatures. It has been found that, withproper use of the alkaline earth metal oxide desiccant, properincremental addition of the catalyst for the NCO/OH and NCO/waterreactions, seriatim addition (in appropriate amounts and sequences) ofcertain aliphatic and aromatic polyisocyanates, and proper selection ofthe polyol, randomness of the prepolymer-forming reactions can beminimized, energy input requirements can be reduced or eliminated,simple equipment can be used, side reactions with moisture and strippingof unreacted isocyanate can be avoided, and adequate control over theviscosity of the prepolymer product can be obtained. Furthermore, theprepolymer product can then be capable of moisture curing to acolor-stable elastomer with the desired properties. The elastomer can becellular, if desired, but is preferrably non-cellular for most of theuses contemplated for this invention. Moisture cure rates are reasonablyrapid to a depth of mils (0.3mm) or more, e.g. up to 65 mils (1.6mm). Acoating, moisture cured according to the teachings of this invention andtested separate from its substrate, exhibits good solid elastomericproperties, e.g. a tensile strength at break greater than 25 p.s.i.(1.75 kg/cm) and an elongation at break greater than 200%. Typically,these cured elastomers have an ultimate tensile strength in excess of100 psi. and an elongation at break in excess of 500%. The prepolymersystems pro- 4 vided according to the teachings of this invention areparticularly useful for coating roof decks and provide an unusuallyweather-resistant, durable roofing material.

DEFINITIONS As used in this application, the below-listed terms have thefollowing meanings:

l. Active hydrogen" is considered to be defined according to theZerwitinoff test described in J. Amer. Chem. Soc. 49, 3181 (1927). Atypical example of an active hydrogen" atom is the hydrogen in thehydroxyl radicals of monoor polyfunctional alcohols. As is known in theart, a wide variety of other substituents such as mercaptans, amines,and acids (e.g. carboxylic acids) contain active hydrogen".

2. Aromatic polyisocyanate" refers to monoor polycyclic aromaticcompounds wherein the NCO radicals are substituted directly on one ormore aromatic rings. Compounds wherein the NCO is insulated" from thearomatic ring by a methylene or higher alkylene group are not consideredaromatic polyisocyanates".

3. Aliphatic polyisocyanates" include the alicyclic and cycloaliphaticpolyisocyanates wherein the NCO radicals are directly substituted on analicyclic aliphatic or cycloaliphatic radical or nucleus, even thoughthe compound may also contain aromatic groups.

4. TDI" refers to tolylene diisocyanate, sometimes called toluenediisocyanate. Isomers of tolylene diisocyanate are indicated thus: "2,4-TDI", "2, 6-TDI", etc.

5. IPDI" refers to isophorone diisocyanate, also known as3-isocyanatomethyl 3, 5, 5 trimethylcyclohexyl isocyanate.

6. Percent solids is a term borrowed from paint chemistry and polyesterresin coating technology. The term refers to the amount of material (beit solid or liquid) remaining after volatile materials or materials notparticipating in the curing of the composition are removed. Thus, forexample, a moisture-curable polyurethane prepolymer composition whichwas prepolymer, 5% pigment, and 10% organic solvent or inert organicliquid diluent would be characterized as a solids" composition, sincethe solvent or diluent would evaporate from the prepolymer during acuring step and/or would not participate in the curing reactions.

7. The term elastomer (hence the term elastomeric") is intended toincorporate by reference the definition used by the American Society forTesting and Materials (A.S.T.M. Elastomeric behavior and properties suchas tensile strength, elongation, and modulus can be measured withstandard tensile testers (e.g. the lnstron") in accordence with knownprocedures.

DETAILED DESCRIPTION As will be clear from the foregoing disclosure,this invention involves careful selection of prepolymerforming materialsand process conditions or steps. The raw materials for the process willbe described in detail first.

POLYOLS The polyols used to make polyurethane prepolymers of thisinvention are preferrably of the polyether, i.e. polyoxyalkylene type.That is, the polyol should contain at least one polyoxyalkylene chainhaving several (e.g. more than or oxyalkylene units. Polyether polyolswhich also contain polyester or polythioether units or the like can beused, so long as the ultimate desired properties for the prepolyrner andthe cured elastomer are obtained. Polyester polyols are ordinarily notpreferred due to the relatively higher stiffness of polyesterurethaneelastomers, particularly at low temperatures. (The polyetherurethanesare generally outstanding in terms of low temperature flexibilityproperties.)

Polyoxyalkylene polyols are commercially available and are made in awell known manner from alkylene oxides and/or tetrahydrofuran throughpolymerization, starting with an initial skeleton or nucleus, which istypically an alcohol or amine of any desired functionality, e.g.propylene glycol, ethylene glycol, trimethylol propane, glycerin,pentaerithritol, ethylene diamine, etc. The most readily availablepolyether polyols are made up of oxyalkylene units containing two,three, or four carbon atoms, e.g. oxyethylene, oxypropylene (both 1, 2-and l, 3-, the l, 2- being more common), and oxybutylene, including bothtetramethylene oxide and l, 2- butylene oxide. As is well known in theart, primary alcohol groups react more rapidly with NCO than secondaryalcohol groups; however, urethanes derived from NCO reactions withsecondary alcohols tend to be somewhat more resistant to degradation(e.g. hydrolytic attack), and the polyoxypropylene glycols tend to bemore resistant to bacterial attack.

The molecular weight, equivalent weight, and functionality of the polyolshould be selected so as to provide a polyurethane prepolyrner with amanageable viscosity and a polyurethane elastomeric moisture-curedproduct with adequate tensile strength and elongation properties. Forexample, a polyether polyol with a molecular weight of [0,000 or higherresults in an NCO- terminated prepolyrner which has an excessiveviscosity at room temperature and is not particularly well suited to theprocess of this invention. Accordingly, a triol with an equivalentweight higher than 3,300, a diol with an equivalent weight higher than5,000, or a tetrol with an equivalent weight higher than 2,000 can besomewhat difficult to work with. On the other hand, the isocyanateequivalent weight of the resulting prepolymer should be at least about1,000 (e.g. 1500-2500) to provide adequate elastomeric properties in thecured product.

It can be an oversimplification to describe the polyol used in thisinvention as a diol", triol", or "tetrol". It would be more accurate torefer to a polyol component which can be a mixture of polyols having anaverage functionality greater than 2 but, typically, less than 4 andpreferably no greater than about 3. Thus, the polyol component can be amixture ofa diol and a triol. It can also be a triol which has beenpartially capped with an agent monofunctional with respect to reactivehydroxyl groups, e.g. a monoisocyanate, a carboxylic acid anhydride orchloride, an alkoxide-forming compound, or the like, which can provide asmall percentage of terminal monourethanes, monoethers, monoesters, etc.for lowering the functionality of the polyol slightly below 3.0 or evenas low as 2.5. In the manufacture of some very high molecular weightpolyols, conditions favoring the formation of some terminal ether (i.e.alkoxy) groups can be provided, obviating the need for a specificcapping step.

As will be explained subsequently, however, the preferred technique ofthis invention is to reduce the functionality of the polyurethaneprepolyrner with a mono functional alcohol, so that a commerciallyavailable polyether triol or the like can be used as a starting materialfor the prepolymer.

Although it is permissible to include incidental amounts of lowmolecular weight polyol or polyamine chain extenders and cross linkersin the reaction mixture which produces the prepolymer, this technique isnot preferred for the practice of this invention. The preferred practiceis to use an essentially polyether triol component having an equivalentweight within the range of 1,000-3,000 or, less preferably, a mixture ofa triol and a diol, e.g. a triol or molecular weight 4,500 mixed with adiol of molecular weight 4,000. Excellent results can be obtained withtriol alone, e.g. Pluracol" 380 (trademark of Wyandotte). The amount ofpolyol component should be selected so as to provide an NCO/OH ratio inthe prepolymer-forming mixture which is preferably greater than aboutl.8:l but less than 3: l. in view of the need to minimize randomreactions in the prepolymer-forming reaction mixture, there is generallyno advantage in going much below 2:1 or much above 2.5:l in NCO/OHratio. However, a slight excess over 2:l, e.g. 2.04:l to 2.25: I, can beuseful.

DEWATERING AGENTS AND FILLERS The dessicant for the polyol and theresulting polyurethane prepolymer is, in the context of this invention,more accurately described as a dc-watering agent". The preferredde-watering agent is calcium oxide, which is white in color and forms ahydroxide which is also white in color. This oxide does not merely takeup water or form a hydrate salt; it actually scavenges water through"slaking reaction, which results in the formation of a hydroxide whichis thermally stable up to about 580C. and, except for some accelerationof curing, behaves substantially as an inert filler in polyurethaneprepolyrner systems. The slaked" de-watering agent will thus notordinarily release chemically bound water through reversal of theslaking reaction. The calcium oxide de-watering agent effectivelyscavenges water not only from the polyol but also from water ofhydration or physically bound water contained in fillers, extenders,pigments, and hygroscopic catalysts included in the prepolymercomposition. To a small extent, the de-watering agent helps to protectthe prepolymer composition against premature gelation due tocontamination with atmospheric moisture; however, the preferredtechnique for protection against moisture contamination will bedescribed subsequently.

An important advantage of calcium oxide is that it appears to providefast, effective water scavenging within a level of alkalinity whichcontributes to the alkaline environment desired for rapid moisture cureof the prepolymer, without contributing to degradative side reactions orthe like. As is known in the art, calcium oxide can be used to de-watera variety of organic compounds, including amines used in two-partpolyurethane systems. see U.S. Pat. No. 3,463,748. Due to its whitecolor (about as white as calcium carbonate), calcium oxide has been usedas a pigment (e.g. a tackreducing pigment) in urethane systems; see, forexample, U.S. Pat. No. 3,075,926, column 5, line 33. How ever, eachurethane system (e.g. one-part vs. two-part, amine cure vs. moisturecure, etc.) presents different formulating considerations with respectto cure rate, side effects in the presence of catalysts, curingmechanisms, etc. It has been observed that basic materials (includingfillers or catalysts) added to the urethane system can sometimes resultin discoloration of the final cured product and other undesirableeffects. For example, it has been observed that sodium hydroxide, bariumoxide or hydroxide, and even high-pH calcium carbonate fillers can causeyellowing.

Oxides of other alkaline earth metals are technically capable of wateruptake but are also capable of forming thermally decomposable hydratesalts such as strontium hydroxide octahydrate. Alkaline earth oxidesoutside the Group IlA atomic weight range of 40 to 138 are notconsidered to have suitable water scavenging properties. In the contextof this invention, CaO is chemically unique as compared to other calciumsalts, other alkaline earth metal oxides, the alkali metal oxides. andthe Group "B and [HA metal oxides.

Any of the conventional fillers, extenders, and pigments, both organicand inorganic, which are essentially inert toward isocyanate radicals oractive hydrogen-containing substituents can be used in this invention,Even those fillers, extenders, and pigments which contain some water(e.g. loosely bound water of hydration) can also be used, since thede-watering agent will scavenge this water before it has an opportunityto react with the polyisocyanate component of the prepolymer-formingreaction mixture. Thus, inorganic salt or oxide fillers and extendersneed not be excluded merely because they contain some water of hydrationor physically bound water. The preferred filler is neutral (as opposedto high-pH) calcium carbonate (e.g. ground limestone) and the preferredwhite pigment is titanium dioxide, but clay, alumina, barium sulfate,calcium sulfate, and other substantially water insoluble salts, oxides,and silicates can be used. Flame retardants and/or inexpensive organicextenders such as powdered vinyl, powdered scrap rubber (natural orsynthetic), and other readily available, substantially inert materialsof this type can be useful. Both white and colored pigments can be usedalone and in combination.

All de-watering agents, fillers, pigments, and extenders useful in thisinvention are ordinarily available in particulate form, eg at least -l2mesh (U.S. or Tyler) and even down to 3 25 me sh (as in the case oftitanium dioxide, clay, and precipitated materials such as precipitatedcalcium carbonate).

The de-watering agent should be used in excess of the amount needed toscavenge all the water present in the prepolymer-forming reactants. Forexample, the polyol component typically contains less than 0.1% byweight of water, and the amount of water contained in calcium carbonateand titanium dioxide is ordinarily no larger and may even be less.Assuming a stoichiometric amount of about 3 parts by weight of calciumoxide per part by weight of water, the excess over stoichiometric forthe calcium oxide can easily be 50 or 100% with no substantial risk ofundesired side reactions, discoloration, degradation of the curedpolymer, etc. In fact, for efficient de-watering it is preferred to useat least 3-l00 times stoichiometry based on the amount of water presentin the prepolymer-forming composition. There does not appear to be anyadvantage in using more than 1000 times stoichiometry, however.

POLYISOCYANATES The present invention makes use of the properties ofaliphatic and aromatic polyfunctional isocyanates, preferablydiisocyanates. For any polyisocyanate molecule used in this invention,it is preferred that at least one of the two or three isocyanateradicals linked to the molecule be substantially kinetically morereactive with respect to active hydrogen than any other free isocyanateradical on the same molecule. Such differences in reaction rate betweenNCO radicals can most easily be provided by having one substantiallyunhindered isocyanate radical on the molecule, the other isocyanateradicals being sterically hindered by a neighboring substituent or thelike. Other techniques for providing differences in reactivity areknown, For example, it is possible to react one equivalent of isocyanatewith an unstable blocking group (e.g. by using phenol as the reversiblecapping agent), but ordinarily this technique does not provide as high alevel of control over results. Another approach, described in US. Pat.No. 3,663,5l4, is to partially hydrogenate a bicyclic aromaticdiisocyanate, so that one of the two aromatic rings is converted to acycloaliphatic nucleus. However, it is unnecessary to use this highlysophisticated type of hybrid molecule. Commercially available aromaticand aliphatic diisocyanates, properly used in accordance with theteachings of this invention, appear to provide all the desiredadvantages of low cost, simple ambient temperature batch or continuousprocessing, minimal random or undesired reactions (e.g. minimalchain-extension) during prepolymer formation, low viscosity in theresulting prepolymer-containing product, dependable and rapid moisturecure of this prepolymer product, and a variety of desired properties inthe moisture-cured material, including color stability, stableelastomeric properties well suited for roofing material, andnon-chalking of pigments after outdoor exposure.

With the exception of pigment and color stability (e.g. resistance ofchalking and ultraviolet-induced degradation), many of these propertiescan be obtained and even maximized by using as much aromaticdiisocyanate as possible, However, if the ratio of aromatic NCOequivalents to aliphatic NCO equivalents exceeds about 7:1, the risk ofcolor instability in the moisture cured urethane polymer can besignificant. Accordingly, this ratio of aromatic NCO/aliphatic NCO ispreferably 6:l or less. With respect to the elastomeric properties ofthe cured urethane, it is preferred that the aromatic NCO/aliphatic NCOratio be at least lzl, preferably 2:1 or more. At the present time,there is also a cost advantage in minimizing the amount of aliphaticdiisocyanate used to make the prepolymer.

The aliphatic polyisocyanate used in this invention can contain two orthree free NCO radicals, the best results being obtained with aliphaticdiisocyanates. [t is preferred that at least one of the free NCO's ofthe aliphatic diisocyanate be hindered by its position on acycloaliphatic ring structure or by a neighboring substituent such as analkyl group. Thus, an alicyclic aliphatic diisocyanate such as analkylene diisocyanate is suitable for use in this invention, if thealkylene chain is appropriately substituted with methyl or ethyl groupsor the like. An example of such a compound is trimethylhexamethylenediisocyanate. An even more preferred approach is to use a cycloaliphaticdiisocyanate such as [PDI" (see the foregoing definitions). The compound[FBI is presently available on a commercial scale at 99.0 weight minimumpurity. The low viscosity and low vapor pressure of this compound areadvantageous from a handling and toxicity standpoint.

Aliphatic diisocyanate molecules wherein both NCO's are substantiallyindistinguishable in their rate of reaction with active hydrogen (e.g.hexamethylene diisocyanate or fully hydrogenated diphenylmethanediisocyante) are generally unsuitable for making prepolymers of thisinvention and are preferably not used in greater than incidentalamounts.

The considerations which apply to the aromatic diisocyanates areanalogous to those relating to the aliphatic diisocyanates. Sterichindrance caused by a substituent of the aromatic ring is the preferredapproach for obtaining the difference in reactivity between the NCOs.Again, both diisocyanates and triisocyanates can be operative, butdiisocyanates are greatly preferred. The aromatic polyisocyanates cancontain 1, 2, or 3 aromatic rings, the monoand bi-cyclic aromatics beingpreferred.

As is known in the art, compounds such as 2,6-TD1 (see the preceedingDefinitions) and diphenylmethane diisocyanate are characterized by,among other things, isocyanate radicals of substantially equal rates ofreactivity with active hydrogen. Commercially available "TD[ typicallycontains a substantial amount of this 2,6-isomer, which is not preferredfor use in this invention. it is therefore preferred that the 2,4- and2,6-isomers be separated to obtain substantially pure 2,4-TDl. In the2,4-isomer, the 2-isocyanate radical is significantly hindered by themethyl group of the toluene nucleus, as compared to the 4- isocyanate,which is relatively unhindered. Presently, 2,4-TDl is commerciallyavailable as a substantially pure isomer free of greaterthan-incidentalamounts of the 2,6-isomer (e.g. as made by the duPont Company under thetrademark "Hylene-T"). It is this separated 2,4-isomer which ispreferred for use in this invention, despite its higher cost.

CATALYSTS A wide variety of materials are known to speed up the reactionbetween isocyanate radicals and active hydrogen. Some of these catalystsindiscriminantly speed up the reaction between NCO and any source ofactive hydrogen, including water, alcohols, mercapatans, amines, acids,and even amides. Others such as mercuric acetate and phenylmercuricacetates tend to be selective and favor the NCO/alcohol or aminereaction over the NCO/water reaction. Broadly speaking, almost any basicsubstance (particularly a material with an unbonded electron pair) mayhave an accelerating effect on the isocyanate/active hydrogen reaction.Thus, the alkaline earth metal oxide de-watering agent does acceleratethe prepolymer-forming reactions to some extent. This acceleratingeffect is relatively weak compared with the preferred conventionalcatalyst, however.

For the purposes of this invention, the conventional catalysts can begrouped into three broad catagories: metallic salts, organo-metalliccompounds, and organic bases. The metallic salt catalysts are typicallysalts of tin, lead, mercury, or Group VIII metals such as iron. Theorgano-metallic compounds are so-called because they contain at leastone direct carbon-'to-metal bond. The preferred organo-metalliccatalysts are of the organo-tin (1V) or organo-lead type. As in the caseof the metal salt catalysts, compounds containing mercury or 10 GroupVIII elements are also operative, provided that the organo-mercurics areused for prepolymer formation and not catalysts of the moisture cure.

A particularly preferred type of catalyst has the formula R,Sn(OCOR'),,wherein R and R are organic (preferably aliphatic) groups. One suchcompound, dibutyl tin dilaurate is readily available and is commonlyabbreviated DBTDL. These organo-tin compounds accelerate both the NCO/OHand NCO/water reactions and will thus do double duty in the context ofthe present invention. That is, the organo-tin catalyst can be added tothe prepolymer-forming forming mixture to accelerate the formation ofurethane linkages from Ol-ls and NCOs and will also serve to acceleratethe moisture cure of the prepolymer-containing product. (Although thereis some debate about the exact mechanism of a moisture cure, terminalNCO groups are apparently converted by water to primary amines whichreact with other NCOs to yield urea linkages.)

It is generally not preferred to use organic bases such as tertiaryamines for the prepolymer-forming reactions of this invention. Thetertiary amines are, however, very useful additives to theprepolymer-containing product, since they are very effective inaccelerating the isocyanate/water reaction.

As is known in the art, the combination of an organotin catalyst with atertiary amine catalyst is an extremely efficient system for speeding upthe moisture cure of a one-part urethane system. Theoretical studieshave shown that one of the most effective tertiary amines for thiscombination of catalysts is commonly referred to as triethylene diamine,also known as 1,4- diaza(2,2,2)-bicyclo-octane.

Many other tertiary amines are suitable for use in this invention,including the trialkylamines (e.g. triethylamine), N-substitutedpiperidine, N,N'-substituted piperazine (e. g. dimethylpiperazine) andthe aromatic heterocyclic tertiary amines such as pyridine.

As will be explained subsequently, the catalyst of this invention ispreferably added in two or more increments. A relatively small incrementis added for the prepolymer-forming reactions, and the balance of thecatalyst or catalytic system is added to the resultingprepolymer-containing product to speed up the moisture cure when theproduct is put to use. As will be clear from the foregoing disclosure,it is preferred to use an organo-metallic catalyst alone for theprepolymer-forming reactions and an organo-metallic catalyst incombination with a tertiary amine for the moisture cure. The organometallic catalyst added in the different stages of the process can bethe same or different. For purposes of convenience of manufacture, asmall amount of a catalyst such as DBTDL is added for formation of theprepolymer, and more DBTDL is added later when the prepolymer-formingreactions are substantially complete. The tertiary amine can be added atthe same time with this further addition of DBTDL or at any othersuitable time after addition of all the polyisocyanates and prior todrumming, canning, bottling, or other packaging of the complete one-parturethane system.

ORGANIC LIQUID DILUENTS AND OTHER INGREDIENTS it is a preferred featureof this invention that the onepart urethanes system is at a high percentsolids" level, e.g. at least solids and preferably at least solids byweight. Thus, the polyols and polyisocya- 1 1 nates used in reactionmixtures of this invention, alone and in combination. should be lowenough in viscosity to avoid the need for solvents. Similarly, theresulting prepolymer. alone or in combination with the de-wateringagent, fillers, and catalysts, should also be low enough in viscosity tobe flowable (e.g. pumpable, pourable or castable) at normal ambienttemperatures.

It is nevertheless a preferred practice of this invention to add a smallamount of organic solvent or organic liquid diluent, not so much toreduce viscosity as to provide the nearly 100% solids one-part urethanesystem with a measurable vapor pressure under normal ambient conditionsof handling, packaging, and storage. The organic liquid diluent ispreferably compatible with the one-part system, e.g. a suitable organicsolvent for the prepolymer. The diluent, being at least slightlyvolatile under normal conditions of handling and storage, helps protectagainst moisture contamination of the one-part urethane system. Byadding the liquid diluent initially or at some other convenient stage ofthe process prior to packaging (drumming, canning, or the like), the useof a dry nitrogen blanket during or just prior to packaging can beavoided.

The preferred organic liquid diluents have a measurable vapor pressureat 20C. pressure and preferably also a measurable vapor pressure even atC. This vapor pressure will keep the contents of a drum or othercontainer of one-part urethane under sufficient pressure to preventatmospheric water vapor from entering the container. Liquids of highvolatility are not needed for this purpose, however. Petroleumdistillates, coal tar distillates, or other substantiallyhydrocarbonaceous liquids boiling at higher than 30C. (e.g. up to 210C.)under atmospheric pressure can be used to provide the necessary vaporpressure in the one-part urethane system. Typical examples of high flashpoint, high boiling diluents are mineral spirits, or petroleum naphtha,solvent naphtha, V.M. and P. naphtha, and high boiling aromatics (e.g.xylene), all of which boil at temperatures above 90C., e.g. up to 175C,preferably less than l50C. The distillates with a flash point above 80F.(27C.) typically contain paraffins, cycloparaffins, and aromatics.

Some of the more polar solvents can also be used, provided they are freeof active hydrogen or other functional groups reactive with eitheractive hydrogen or isocyanate. Among these are the halogenated solvents. Ketones are less suitable due to the possibility of sidereactions with the prepolymer-forming reactants.

Other additives or modifiers for the prepolymer composition which can beuseful include platicizers, dispersion aids, foaming or cell-controlagents (if a foam is desired), de-gassing agents, pH-adjusting agents,and other additives suitable for elastomeric coatings of moldedarticles.

ISOCYANATE CAPPING AGENTS As will be explained subsequently, when theisocyanate functionality of a prepolymer of this invention is about 3.0or more, this functionality is preferably reduced slightly throughreaction with a active hydrogencontaining monofunctional capping agentsuch as a monofunctional alcohol, a monocarboxylic acid, amonomercaptan, or a monofunctional secondary amine. The preferredcapping agents are the monofunctional aliphatic alcohols, preferably theliquid alcohols (such as lower alkanols) miscible with the prepolymercomposition and with the desired tertiary amine 12 catalyst. Thus, thepreferred lower alkanols contain 12 carbon atoms or less, e.g. n-butylalcohol, which is compatible with triethylene diamine. The optimumisocyanate functionality of the prepolymer composition (e.g. for aroofing seal coat) is about 2.5 to about 2.8.

THE PROCESS The process of this invention can be carried out on batch,continuous, or semi-continuous basis, depending on the type of rawmaterial metering and conveying equipment, product recovery andpackaging arrangement, etc. In its broadest aspect, this processcomprises the following steps.

First, an isocyanate-reactive composition is provided. This compositioncontains the polyol, the de-watering agent, a catalyst (preferably anorgano-metallic catalyst for both the NCO/OH and NCO/water reactions),fillers (if desired), any desired modifiers (e.g. de-gassers), pigments(if desired), and a small amount of inert organic liquid diluent (ifdesired). This isocyanatereactive composition should be low enough inviscosity to permit stirring with conventional mixing equipment atnormal ambient temperatures. The organic liquid diluent (naphtha,mineral spirits, etc.) does reduce the viscosity slightly, but isordinarily not essential for viscosity reduction. Thisisocyanate-reactive, polyol containing composition is mixed or agitated(eg for 0.5-5 hours, preferably l-2 hours) until the water scavengingreaction is substantially complete. Water scavenging can be carried outat room temperature or at mildly elevated temperatures, if desired (e.g.up to 50C.). The progress of this scavenging or slaking reaction can bemonitored with a distillation test and/or a Karl Fischer titration. Theisocyanate-reactive composition can be blended in a kettle equipped witha stirrer or in a horizontal churn or mixer.

Second, the aliphatic polyisocyanate is then added to the bone-dryisocyanate-reactive composition. Optionally, the organo-metalliccatalyst can be added with the aliphatic polyisocyanate. Preferably, noheat is applied to the resulting reaction mixture, but startingmaterials and mixtures there of can be maintained at any convenient,normal in-plant ambient temperature (e.g. l5-45C). The essentiallyadiabatic exotherm produced by the isocyanate-polyol reaction providessufficient heat to raise the reaction mixture a few degrees C. Theexotherm should be carefully monitored, since it provides a good measureof the amount ofhead start" allowed to the aliphatic polyisocyanatebefore the aromatic polyisocyanate is added. The desired amount ofexotherm varies with the equivalent weight of the polyol. For a polyolhaving an equivalent weight in the range of 1500-2300 (e.g. 1700-2000),an exotherm of about 3-5C. indicates that more than 25% of the aliphaticisocyanate equivalents have reacted with the polyol, the theoreticalideal being about 50% for a diisocyanate. An exotherm of, say, P or 2C.would typically indicate too many unreacted equivalents of aliphaticisocyanate, leaving the possibility that the aromatic polyisocyanate,when added, can enter into a random series of reactions including somechain extension of isocyanate-terminated prepolymer molecules. Suchchain extension may increase the viscosity of the reaction mixture to anundesired level, but, more important, it results in the conversion ofaromatic isocyanate equivalents into undesired urethane linkages. Anexotherm in excess of about 5C. oftentimes indicates too much of a headstart for the aliphatic polyisocya- 13 nate, which can result inexcessive viscosity increases due to random reactions.

Third, preferably after at least 25% of the aliphatic isocyanateequivalents (more preferably about 40-60%) have reacted, the aromaticpolyisocyanate is then added, resulting in a much greater exotherm,which tends to appraoch a fairly constant temperature, indicating thatthe isocyanate/polyol reaction is substantially completed. After a totalpolyol/NCO reaction time of, typically, 3-60 minutes and a totalexotherm of, for example, 1020C., the result is an isocyanateterminatedpolyurethane prepolymer with a managable viscosity. In the preferredpractice of this invention, the molecular weight of eachprepolymermolecule tends to be about equal to the one hydroxylequivalent weight plus two isocyanate equivalent weights times thefunctionality of the polyol indicating minimal chain extension andunreacted polyisocyanate.

Fourth, the catalyst for the moisture cure reaction is preferably notadded to the reaction mixture until isocyanate/polyol reaction appearsto be complete or substanially complete. This is particularly true oftertiary amine catalysts. A preferred practice is to add some organo-tincatalyst (e.g. 003-1 .0 wt. or about 25 to 80% of the total included inthe final prepolymer composition) in the early stages of the process,and the balance with the moisture cure catalyst just prior to packaging.As pointed out previously, the preferred moisture cure catalyst is acombination of a tertiary amine and an organo-metallic catalyst. At thisstage of the process, the isocyanate functionality of the prepolymercomposition can be reduced slightly with one of the monofunctionalcapping agents described previously. If the functionality of the systemwas properly adjusted at some earlier stage, this capping step can beomitted.

Fifth, the prepolymer composition is now at a fairly low viscosity dueto the high internal temperature created by the exothermic NCO/activehydrogen reactions. (The capping step, if used, also contributes anexotherm.) It is therefore preferred to package the prepolymercomposition while it is still hot and will readily flow into containers,thus speeding up the packaging operation. The organic liquid diluent,added earlier in the process, protects the prepolymer composition fromgaseous atmospheric contaminants (e.g. water vapor) during and afterpackaging. The containers for the prepolymer are provided with ahermetic seal for the con tents and are made as moisture tight aspossible. An entire batch, from charging of the polyol to the mixer upto this packaging step takes less than hours, e.g. 2 to 3 hours. Thesealed containers can be shipped to the job and used in coating or otherapplications or techniques, including simple pouring, trowelling,casting, spraying, brushing, etc.

A coating of the prepolymer composition cures to a depth of -200 mils(e.g. 65 mils) under normal atmospheric temperature and humidityconditions to form an elastomeric layer which, tested separate from itssubstrate, preferably has a tensile strength at break of 50-300 psi andan elongation at break of 5002000%. A tensile strength in excess of I00psi (e.g. up to 200 psi) and an elongation in excess of 800% (e.g. up tol500%) is particularly well suited for the primary seal for a roof deckor as a top coat for an existing roof. Asphalt coatings, by comparison,are non-elastomeric and have a relatively negligible elongation atbreak. Both the coating and curing operations are rapid and efficient.For example, a one-part, moisture-curable prepolymer composition with aviscosity less than 300,000 centipoise at 25C. can be trowelled, pumpedand sprayed, cast, or otherwise coated at about 3-5 gallons per 100square feet and will form a firm gel to a depth of 65 mils in 3-l2hours, depending on the ambient conditions.

In the above-described second and third steps of this process, the idealreaction scheme (assuming, for simplicity of explanation, that thepolyol is 100% triol) would be as follows: 1 mole of aliphaticdiisocyanate reacts with l mole of triol to yield a molecule containing1 free aliphatic isocyanate radical and 2 free hydroxyl radicals. Thearomatic diisocyanate is then added, resulting in the formation of asingle-unit prepolymer having a molecular weight equal to the molecularweight of the triol plus the molecular weight of one aliphaticdiisocyanate and two aromatic diisocyanates, e.g. a molecular weight ofabout 50009000, preferably 6000-7000. When the single unit prepolymer ismoisture cured, the aromatic isocyanates theoretically are completely oralmost completely converted to urea linkages and are buried" in themiddle of polymer chains and branches. Aromatic-amine termination ofpolymer chains and branches is rare, hence discoloration under theinfluence of light is unlikely most of the amine termination beingaliphatic rather than aromatic in character.

Needless to say, this theoretical model is difficult to obtain inpractice. Nevertheless, this invention appears to provide a very closeapproximation of the theoretical model throughout the disclosed rangesof NCO/OH ratios and aromatic NCO/aliphatic NCO ratios. As pointed outpreviously, a slight excess over the theoretical 2:1 NCO/OH ratioappears to provide optimum results. Whatever the NCO/OH ratio,ordinarily 2/7 to 5/6 NCO equivalents of aliphatic diisocyanate arepreferably used, the balance being aromatic diisocyanate. Excellentresults have been obtained with a 2:1 weight ratio of TDI t0 IPDI whichcorresponds to approximately a 2.5:l molar ratio.

The viscosity of resulting prepolymer-containing composition can easilybe kept below 800,000 centipoise (cps) at 25C., (Brookfield HAFviscometer, spindle No. 5 at l rpm) even at l00% solids. Viscosities ofl5,000300,000 cps have been obtained in practice, depending on the exactformulations used to make the prepolymer composition. The viscosity ofthe one-part system appears to be stable indefinitely, so long as thesystem is protected from contact or contamination with moisture or othersources of active hydrogen.

When the aforementioned capping step is used to adjust the functionalityof the resulting isocyanate-terminated prepolymer, it is convenient toadd the tertiary amine blended with a lower alkanol capping agent. Inthis invention, there does not appear to be any difficulty connectedwith using tertiary amine/organometallic moisture cure catalysts.

USES OF THE PREPOLYMER COMPOSITION Prepolymer compositions of thisinvention can be coated or molded and cured to form elastomeric coatingsor articles, which can be either cellular or non-cel- Iular. To producea cellular article such as a foamed cushioning material or the like,water can be used as both the curing or foaming agent, or, if desired, ablowing agent such as a fluoroalkane can be used. The high solids.relatively low viscosity character of the prepolymer compositionfacilitates casting and pouring without entailing the hazards andinconveniences of solvent evaporation or recovery. Although thepreferred application of these prepolymer materials is in the field ofroofing (both primary seals and top coats) other areas of applicationinclude waterproofing, vapor barrier coatings or treatments or seals forthe construction industry generally, fabric coating, marine coatings.thermally insulative coatings (particularly when the polymer is foamed).seamless tank linings resistant to water and mild reagents, sealants,molded or coated pre-fabricated panels, and the like. To form stiff,paste-like sealants, a relatively low viscosity prepolymer system can bethickened with inert conventional thickening agents (colloidalsilica,bentonite. etc.), if desired. Noncellular coatings preferablyrange from 1 to 200 mils (.03-5mm) in thickness, typically 10-100 mils(0.3-2.5mm). if a high tensile-strength, low elongation elastomer isdesired, (e.g. tensile strength in excess of 250 psi, elongation lessthan about 400%), a prepolymer with an isocyanate functionality slightlyin excess of 3.0 can be used. If a high elongation, low tensile strengthpolymer is desired, the prepolymer functionality can be reduced to 2.0or slightly higher. As pointed out previously, the preferred properties(e.g. l200 psi tensile, 8001500% elongation) are considered to beachieved with a prepolymer functionality slightly less than 3.0.Properties of the cured elastomer can be tailored to various needsthrough, for example, different ratios of aromatic-to-aliphaticpolyisocyanate. Aliphatic polyisocyanates can be maximized, for example,when speed of moisture cure and tensile strength are not important.Aromatic diisocyanates can be maximized when color stability andnon-chalking are less important than the toughness of the polymer.

In the following examples all parts and percentages are by weight unlessotherwise indicated.

EXAMPLE 1 A moisture-curable, low viscosity isocyanate-terminated,filled and pigmented polyetherurethane prepolymer was prepared from thefollowing total composition:

Component and Description Parts/wt.

A. TPE-4542--(a trifunctional aliphatic polyether polyol of molecularwtv 4500 and containing some primary and some secondary hydroxyl groups.

Typical hydroxyl number 37.3 and typical water content 0.04%lwt.)17.0124

B. "TP-4020P"--(a difunctional aliphatic polyetber polyol of molecularwt. approximately 4000 and containing some non-reactive constituents.

Typical hydroxyl number 28.8 and typical water content 0.01%lwt.)43.9508

C. Essentially neutral. water ground limestone (calcium carbonate)filler (contains some water). 99% minus 325 mesh (U.S.) 12.9508

D. White Pigment (Titanium dioxide) 3.8773

E. Petroleum Naptha. boiling range F. Dibutyl tin dilaurate (catalyst,

added in l increment) 0.0538

G. Silicone dispersion aide 0.0852

H. Phosphate ester plasticizer 1.7996

Jv Calcium oxide 12.8773

K. 2,4'TDl 4.3111

L. lPDl (see US. Patent 3.549.569) 2.5734

The procedure for blending these ingredients and forming a prepolymercomposition was as follows: Components A and B were charged to ahorizontal churn, the entire amount of both components A and B beingadded. The entire amount of components C, D, E, G, H, and .l were addedto the churn containing components A and B. The entire amount ofcomponent F was also added to the resulting mixture; however. the totalamount of component F can be brought up to as much as 1.0 or 2.0 partsafter the prepolymer has been formed. The mixture of components Athrough .1 was continuously mixed for 2 hours at normal ambienttemperatures, at which time a distillation-type water determination testindicated that scavenging of the water by the calcium oxide (componentJ) was complete. Components K and L were then simultaneously added withthe mixture initially at room temperature. (As will be shown in Example2, the preferred procedure is to add component L first.) In less than 35minutes, the isocyanate-terminated prepolymer adduct was formed. asindicated by a leveling off of the temperature rise amounting to 27.5F.(At this point, additional component F or component F blended withtriethylene diamine or N,N'-dimethyl piperazine can be added and thecomposition can be canned in sealed containers.)

Prior to coating and curing, the prepolymer composition (99.1% solids)was found to have a viscosity of 26,000 centipoise at 77F.

After coating and curing the prepolymer composition, a 65 mil film ofthe resulting polyurethane elastomer was stripped from the substrate andtested. The following properties were observed:

Ultimate tensile strength (at break): 150 psi.

Elongation: |300%.

Atlas Twin-arc Weatherometer Test: no change after 400 hours.

EXAMPLE 2 The composition and procedure of Example 1 were repeated withsome exceptions, the principal exception being the elimination of dioland the use of the head start" technique, wherein IPDl (component L) isadded before 2,4-TDl (component K).

Thus. in this Example:

a. A poly(oxypropylene) trio] of 6700 molecular weight (Pluracol"380)was substituted for component A and B.

b. Mineral spirits were substituted for component E.

c. The substantially neutral calcium carbonate filler was a low oilabsorption ground limestone which was slightly coarser, minus 200 mesh(U.S.

d. Component F was added in two increments: 0.16

part was added to the polyol-containing mixture along with component L(lPDl) and 0.1 1 part was added after formation of the prepolymer.

. After an exotherm of 4F. had been observed (resulting from thereaction of the polyol component L), component K was added in an amountequal (by weight) to the amount of component L, these amounts being setto provide an NCO/OH ratio of 2.24:1.

f. After the completion of the reaction between the polyol and thepolyisocyanates, N,N' dimethyl piperazine blended with n-butyl alcoholwas added. The amount of butyl alcohol was sufficient to lower theisocyanate functionality of the prepolymer to 2.8.

after coating and curing as in Example I, a 65 mil thickness ofunsupported elastomeric film was found to have a tensile strength atbreak of 130 psi and an elongation of l000%. Thus, similar results wereobtained with this Example without resorting to a blend of triol anddiol. The elastomeric film supports combustion very poorly and does notappear to be a significant fire hazard.

What is claimed is:

l. A process for making a one-part, moisture-reactive compositioncomprising a moisture-reactive isocyanate-terminated polyetherurethaneprepolymer, said process comprising the steps of:

a. providing an isocyanate-reactive composition comprising: an alkalineearth metal oxide, wherein the metal has an atomic weight ranging from40 to [38, a catalyst for isocyanate/active hydrogen reactions, l0% byweight of an organic liquid inert to active hydrogen-bearing andisocyanate radicals,

and a liquid polyol composition having an average equivalent weightgreater than 1000 and an average functionality greater than 2, saidpolyol containing at least one polyoxyalkylene chain; the amount ofalkaline earth metal oxide being at least 50% greater than thestoichiometric amount for reacting with all the water in saidisocyanate-reactive composition; b. exothermically reacting aliphaticpolyisocyanate with said isocyanate-reactive composition, said aliphaticpolyisocyanate being free, except for incidental amounts, of anyaliphatic polyisocyanate having at least two free isocyanate radicals onthe same molecule which are substantially kinetically equal to eachother in their reactivity with respect to active hydrogen;

after at least 25% of the number of equivalents of said aliphaticpolyisocyanate have reacted with said isocyanate-reactive composition,exothermically reacting unreacted active hydrogen in saidisocyanate-reactive composition with aromatic polyisocyanate, saidaromatic polyisocyanate being free, except for incidental amounts, ofany aromatic polyisocyanate having at least two free isocyanate radicalson the same molecule which are substantially kinetically equal to eachother in their reactivity with respect to active hydrogen, the amountsof polyisocyanate being controlled such that the ratio of aromatic NCOequivalents to aliphatic NCO equivalents reacted with saidisocyanate-reactive composition is at least about 121 but less than 7:1and the NCO/OH ratio for the entire moisture curable composition isgreater than about L821 but no more than about 3:1; whereby amoisture-reactive isocyanate-terminated polyurethane prepolymercomposition having an average NCO functionality greater than 1.8 butless than 3.0 is obtained as a result of steps (b) and (c), and wherebythe yield of single-unit, polyurethane prepolymer in said polyurethaneprepolymer composition is maximized, said prepolymer composition, uponthe addition of a curing catalyst for the isocyanate/water reaction,being curable under normal ambient conditions to a solid which, in theform of a sheet-like article, has a tensile strength at break greaterthan 25 psi. 2. A process according to claim 1, wherein saidpolyurethane prepolymer composition is curable under normal ambientconditions to a solid elastomer, which, in

18 the form of a sheet-like article, has an elongation at break greaterthan 200%, and wherein:

a. said alkaline earth metal oxide consists essentially of calcium oxideand the amount of said calcium oxide is at least in excess of thestoichiometric amount for 0.1% by weight of water, based on the weightof said isocyanate-reactive composition; said isocyanate-reactivecomposition further comprises at least one additional ingredientselected from the group consisting of a filler and a pigment, and saidcatalyst for isocyanate/active hydrogen reactions being anorgano-metallic catalyst for at least the NCO/OH reaction;

b. said aliphatic polyisocyanate consists essentially of cycloaliphaticdiisocyanate molecules having one substantially sterically unhinderedfree isocyanate radical and one relatively sterically hindered freeisocyanate radical; said aromatic polyisocyanate consists essentially ofaromatic diisocyanate molecules having I or 2 benzene rings, onesubstantially sterically unhindered free isocyanate radical and onerelatively sterically hindered free isocyanate radical, the molar ratioof said aromatic diisocyanate to said aliphatic diisocyanate being atleast about 2:] but less than about 6:1; the NCO/OH ratio for the entiremoisture curable composition ranging from about 2:1 to about 2.5:]; andsubsequent to the formation of said isocyanate-terminatedpolyetherurethane prepolymer composition according to said step (c) butbefore the curing thereof, a curing catalyst for at least theisocyanate/water reaction is added to provide a one-part compositionwhich is moisture-curable at normal ambient temperatures.

3. A process according to claim 2 wherein said curing catalyst comprisesa tertiary amine.

4. A process according to claim 3 wherein said curing catalyst furthercomprises an organo-metallic compound.

5; A process according to claim 1 wherein said polyol compositioncomprises at least one polyoxyalkylene trio] and has a hydroxylfunctionality less than 4 and wherein the average isocyanatefunctionality of the said isocyanate-terminated polyetherurethaneprepolymer is adjusted to less than 3.0 but greater than 2.0 with amonofunctional alcohol during said step (d) by blending saidmonofunctional alcohol with said curing catalyst.

6. A process according to claim 1 wherein said alkaline earth oxide iscalcium oxide, said aliphatic polyisocyanate consists of substantiallypure isophorone diisocyanate, and said aromatic diisocyanate consists ofsubstantially pure 2,4-tolylene diisocyanate.

7. A process according to claim 1 wherein intermediate and final productyields are maximized in accordance with the following reaction scheme:

each mole of said aliphatic polyisocyanate is reacted with one mole ofsaid liquid polyol composition to yield a compound containing l freealiphatic isocyanate radical and 2 free hydroxyl radicals;

said compound is reacted with said aromatic polyisocyanate to yield asingle unit prepolymer having a molecular weight equal to the molecularweight of said polyol composition and two aromatic polyisocyanates, saidmolecular weight being in the range of about 5000-9000.

8. A process according to claim 1 wherein the combined duration of steps(b) and (c), from the beginning of step (b) to the obtaining of the saidmoisture-reactive isocyanate-terminated polyurethane prepolymercomposition is less than 5 hours.

9. A process for making a moisture-curable polyurethane coatingcomposition having a viscosity less than 800,000 centipoise at 25C. andcontaining an organotin/tertiary amine moisture cure catalyst, saidprocess comprising the steps of:

a. blending, at normal ambient temperatures, the

components comprising: (l a liquid polyoxyalkylene polyol componenthaving an average functionality of at least 2.5 but no greater than 3.0and an equivalent weight greater than 1000 but less than 3300; (2) aminor amount, by weight, of a particulate solid component containing atleast some pigment; (3) an amount of particulate calcium oxide in excessof the amount needed to scavenge all the water in said polyol componentand said filler component and to provide an alkaline environment for theresulting blend of components; (4) 01-10% by weight of a petroleumdistillate which is inert to isocyanate radicals andactive-hydrogen-bearing radicals and has a boiling point greater than30C. and a measurable vapor pressure at C. under normal atmosphericpressure; and (5) no more than about 80% by weight of the total of theorgano-tin component of said organo-tin/tertiary amine catalyst;

b. mixing the resulting blend until the water/calcium oxide reaction iscompleted and all water in the blend has been scavenged;

c. providing a polyurethane reaction mixture by adding without theaddition of heat, 2/7 to 5/6 NCO equivalents of isophorone diisocyanateper equivalent of polyol active hydrogen and permitting an essentiallyadiabatic exotherm to develop until the temperature of the resultingmixture indicates that at least 25% of the isocyanate radicals of theisophorone diisocyanate have been converted to urethane linkages;

d. adding to the resulting polyurethane reaction mixture of step (c),without any further addition of heat, sufficient substantially pure2,4-tolylene diisocyanate to bring said reaction mixture, including bothreacted and unreacted isophorone diisocyanate, to an NCO/OH ratio ofabout 2:l to about 2.5: l and permitting an additional essentiallyadiabatic exotherm to develop until substantially all of the freehydroxyl in said reaction mixture has been converted to urethanelinkages;

e. adding to said reaction mixture: said tertiary amine catalystcomponent of said organo-tin/tertiary amine moisture-cure catalyst andthe balance of said organo-tin catalyst component of saidorganotin/tertiary amine moisture catalyst; and

f. packaging the resulting product in substantially hermetically sealedcontainers; the combined duration of steps (c), (d), and (e) being lessthan 5 hours.

10. A product made by the process of claim 1.

11. A product made by the process of claim 9.

[2. A process for making a moisture-curable polyurethane compositioncomprising the steps of:

a. blending at normal ambient temperatures, the

components comprising (1) a liquid polyoxyalkylene polyol componentcomprising a trio] having an equivalent weight within the range of1000-3300 and a diol with an equivalent weight within the range of1000-5000; (2) an amount of particulate calcium oxide which is 3-l000times the amount needed to scavenge all the water in said polyolcomponent; (3) up to l0% by weight of an inert organic liquid diluenthaving a boiling point in the range of 30l75C. and a flash point above27C., and (4) 0.03-1.05, based on the weight of said coatingcomposition, of an organo-metallic catalyst;

b, mixing the resulting blend until the water/calcium oxide reaction iscompleted and all water in the blend has been scavenged;

c. reacting aliphatic diisocyanate and aromatic diisocyanate with thesaid resulting mixture, said aliphatic diisocyanate and said aromaticdiisocyanate each having one substantially sterically unhindered freeisocyanate and one relatively sterically hindered free isocyanateradical, said aliphatic diisocyanate and said aromatic diisocyanatebeing free, except for incidental amounts, of any diisocyanate whereinboth isocyanate radicals are of substantially kinetically equalreactivity, the resulting NCO/OH ratio being within the range of about2:1 to about 3:] and the molar ratio of aromatic diisocyanate toaliphatic diisocyanate being at least 1:] but less than 7:1; and

d. packaging the resulting product in substantially hermetically sealedcontainers within 5 hours after the beginning of step (c).

13. A process according to claim 12 wherein said moisture-curablepolyurethane composition has a viscosity less than 800,000 centipoise at25C.

14. A process according to claim 13 wherein said moisture-curablepolyurethane composition is a pastelike sealant.

15. In a process for making a moisture-reactive composition comprising amoisture-reactive isocyanate-terminated prepolymer, which processincludes the step of utilizing an alkaline earth metal oxide as adessicant for at least one of the isocyanate-reactive starting materialsfor making said isocyanate-terminated prepolymer, said startingmaterials including a polyoxyalkylene polyol composition having anequivalent weight greater than I000 and an average functionality greaterthan 2; the improvement which comprises:

a. exothermically reacting aliphatic polyisocyanate with saidpolyoxyalkylene polyol composition, said aliphatic polyisocyanate beingfree, except for incidental amounts, of any aliphatic polyisocyanatehaving at least two free isocyanate radicals on the same molecule whichare substantially kinetically equal to each other in their reactivitywith respect to active hydrogen;

b. after at least 25% of the number of equivalents of said aliphaticpolyisocyanate have reacted with said polyoxyalkylene polyolcomposition, exothermically reacting unreacted active hydrogen in saidpolyoxyalkylene polyol composition with aromatic polyisocyanate, saidaromatic polyisocyanate being free, except for incidental amounts, ofany aromatic polyisocyanate having at least two free isocyanate radicalson the same molecule which are substantially kinetically equal to eachother in their reactivity with respect to active hydrogen, the amountsof polyisocyanate being controlled such that the ratio of aromatic NCOequivalents to ali- 22 whereby the yield of single-unit, polyurethaneprepolymer in said polyurethane prepolymer composition is maximized,said prepolymer composition, upon the addition of a curing catalyst forthe isocyanate/water reaction, being a one-part system which is curableunder normal ambient conditions to a solid which, in the form of asheet-like article,

has a tensile strength at break greater than 25 psi.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3 919,173

DATED 1 November 11, 1975 INVENTOR(S) Robert N. Coyner and Peter SkujinsIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown be\ow:

In column 1, line 18, for "90" read 90%-.

In column 6, line 15, for "or" read of-.

In column 9, line 48, for "acetates" read acetate.

In column 10, line 12 delete "forming" In column 20, line 9, for "1.05"read l.O%-.

In column 21, line 3, for "7:1" read 7:l-.

In column 21, line 6, for "terminted" read terminated-.

Signed and Scaled this Nineteenth D a y of Serum)" 1978 [SEAL] A ttest:

RUTH C MASON DONALD W. BANNER Attesting Ojficer Commissioner of Patentsand Trademarks

1. A process for making a one-part, moisture-reactive compositioncomprising a moisture-reactive isocyanate-terminated polyetherurethaneprepolymer, said process comprising the steps of: a. providing anisocyanate-reactive composition comprising: an alkaline earth metaloxide, wherein the metal has an atomic weight ranging from 40 to 138, acatalyst for isocyanate/active hydrogen reactions, 0-10% by weight of anorganic liquid inert tO active hydrogen-bearing and isocyanate radicals,and a liquid polyol composition having an average equivalent weightgreater than 1000 and an average functionality greater than 2, saidpolyol containing at least one polyoxyalkylene chain; the amount ofalkaline earth metal oxide being at least 50% greater than thestoichiometric amount for reacting with all the water in saidisocyanate-reactive composition; b. exothermically reacting aliphaticpolyisocyanate with said isocyanate-reactive composition, said aliphaticpolyisocyanate being free, except for incidental amounts, of anyaliphatic polyisocyanate having at least two free isocyanate radicals onthe same molecule which are substantially kinetically equal to eachother in their reactivity with respect to active hydrogen; c. after atleast 25% of the number of equivalents of said aliphatic polyisocyanatehave reacted with said isocyanate-reactive composition, exothermicallyreacting unreacted active hydrogen in said isocyanate-reactivecomposition with aromatic polyisocyanate, said aromatic polyisocyanatebeing free, except for incidental amounts, of any aromaticpolyisocyanate having at least two free isocyanate radicals on the samemolecule which are substantially kinetically equal to each other intheir reactivity with respect to active hydrogen, the amounts ofpolyisocyanate being controlled such that the ratio of aromatic NCOequivalents to aliphatic NCO equivalents reacted with saidisocyanate-reactive composition is at least about 1:1 but less than 7:1and the NCO/OH ratio for the entire moisture curable composition isgreater than about 1.8:1 but no more than about 3:1; whereby amoisture-reactive isocyanate-terminated polyurethane prepolymercomposition having an average NCO functionality greater than 1.8 butless than 3.0 is obtained as a result of steps (b) and (c), and wherebythe yield of single-unit, polyurethane prepolymer in said polyurethaneprepolymer composition is maximized, said prepolymer composition, uponthe addition of a curing catalyst for the isocyanate/water reaction,being curable under normal ambient conditions to a solid which, in theform of a sheet-like article, has a tensile strength at break greaterthan 25 psi.
 2. A process according to claim 1, wherein saidpolyurethane prepolymer composition is curable under normal ambientconditions to a solid elastomer, which, in the form of a sheet-likearticle, has an elongation at break greater than 200%, and wherein: a.said alkaline earth metal oxide consists essentially of calcium oxideand the amount of said calcium oxide is at least 50% in excess of thestoichiometric amount for 0.1% by weight of water, based on the weightof said isocyanate-reactive composition; said isocyanate-reactivecomposition further comprises at least one additional ingredientselected from the group consisting of a filler and a pigment, and saidcatalyst for isocyanate/active hydrogen reactions being anorgano-metallic catalyst for at least the NCO/OH reaction; b. saidaliphatic polyisocyanate consists essentially of cycloaliphaticdiisocyanate molecules having one substantially sterically unhinderedfree isocyanate radical and one relatively sterically hindered freeisocyanate radical; c. said aromatic polyisocyanate consists essentiallyof aromatic diisocyanate molecules having 1 or 2 benzene rings, onesubstantially sterically unhindered free isocyanate radical and onerelatively sterically hindered free isocyanate radical, the molar ratioof said aromatic diisocyanate to said aliphatic diisocyanate being atleast about 2:1 but less than about 6:1; the NCO/OH ratio for the entiremoisture curable composition ranging from about 2:1 to about 2.5:1; andd. subsequent to the formation of said isocyanate-terminatedpolyetherurethane prepolymer composition according to said step (c) butbefore the curing thereof, a curing catalyst for at least theisocyanate/water reaction is added to provide a one-part compositionwhich is moisture-curable at normal ambient temperatures.
 3. A processaccording to claim 2 wherein said curing catalyst comprises a tertiaryamine.
 4. A process according to claim 3 wherein said curing catalystfurther comprises an organo-metallic compound.
 5. A process according toclaim 1 wherein said polyol composition comprises at least onepolyoxyalkylene triol and has a hydroxyl functionality less than 4 andwherein the average isocyanate functionality of the saidisocyanate-terminated polyetherurethane prepolymer is adjusted to lessthan 3.0 but greater than 2.0 with a monofunctional alcohol during saidstep (d) by blending said monofunctional alcohol with said curingcatalyst.
 6. A process according to claim 1 wherein said alkaline earthoxide is calcium oxide, said aliphatic polyisocyanate consists ofsubstantially pure isophorone diisocyanate, and said aromaticdiisocyanate consists of substantially pure 2,4-tolylene diisocyanate.7. A process according to claim 1 wherein intermediate and final productyields are maximized in accordance with the following reaction scheme:each mole of said aliphatic polyisocyanate is reacted with one mole ofsaid liquid polyol composition to yield a compound containing 1 freealiphatic isocyanate radical and 2 free hydroxyl radicals; said compoundis reacted with said aromatic polyisocyanate to yield a single unitprepolymer having a molecular weight equal to the molecular weight ofsaid polyol composition and two aromatic polyisocyanates, said molecularweight being in the range of about 5000-9000.
 8. A process according toclaim 1 wherein the combined duration of steps (b) and (c), from thebeginning of step (b) to the obtaining of the said moisture-reactiveisocyanate-terminated polyurethane prepolymer composition is less than 5hours.
 9. A process for making a moisture-curable polyurethane coatingcomposition having a viscosity less than 800,000 centipoise at 25*C. andcontaining an organo-tin/tertiary amine moisture cure catalyst, saidprocess comprising the steps of: a. blending, at normal ambienttemperatures, the components comprising: (1) a liquid polyoxyalkylenepolyol component having an average functionality of at least 2.5 but nogreater than 3.0 and an equivalent weight greater than 1000 but lessthan 3300; (2) a minor amount, by weight, of a particulate solidcomponent containing at least some pigment; (3) an amount of particulatecalcium oxide in excess of the amount needed to scavenge all the waterin said polyol component and said filler component and to provide analkaline environment for the resulting blend of components; (4) 0.1-10%by weight of a petroleum distillate which is inert to isocyanateradicals and active-hydrogen-bearing radicals and has a boiling pointgreater than 30*C. and a measurable vapor pressure at 0*C. under normalatmospheric pressure; and (5) no more than about 80% by weight of thetotal of the organo-tin component of said organo-tin/tertiary aminecatalyst; b. mixing the resulting blend until the water/calcium oxidereaction is completed and all water in the blend has been scavenged; c.providing a polyurethane reaction mixture by adding without the additionof heat, 2/7 to 5/6 NCO equivalents of isophorone diisocyanate perequivalent of polyol active hydrogen and permitting an essentiallyadiabatic exotherm to develop until the temperature of the resultingmixture indicates that at least 25% of the isocyanate radicals of theisophorone diisocyanate have been converted to urethane linkages; d.adding to the resulting polyurethane reaction mixture of step (c),without any further addition of heat, sufficient substantially pure2,4-tolylene diisocyanate to bring said reaction mixture, including bothreacted and unreacted isophorone diisocyanate, to an NCO/OH ratio ofabout 2:1 to about 2.5:1, and permitting an additional essentiallyadiabatic exotherm to develop until substantially all of the freehydroxyl in said reaction mixture has been converted to urethanelinkages; e. adding to said reaction mixture: said tertiary aminecatalyst component of said organo-tin/tertiary amine moisture-curecatalyst and the balance of said organo-tin catalyst component of saidorgano-tin/tertiary amine moisture catalyst; and f. packaging theresulting product in substantially hermetically sealed containers; thecombined duration of steps (c), (d), and (e) being less than 5 hours.10. A product made by the process of claim
 1. 11. A product made by theprocess of claim
 9. 12. A process for making a moisture-curablepolyurethane composition comprising the steps of: a. blending at normalambient temperatures, the components comprising (1) a liquidpolyoxyalkylene polyol component comprising a triol having an equivalentweight within the range of 1000-3300 and a diol with an equivalentweight within the range of 1000-5000; (2) an amount of particulatecalcium oxide which is 3-1000 times the amount needed to scavenge allthe water in said polyol component; (3) up to 10% by weight of an inertorganic liquid diluent having a boiling point in the range of 30*-175*C.and a flash point above 27*C., and (4) 0.03- 1.05, based on the weightof said coating composition, of an organo-metallic catalyst; b. mixingthe resulting blend until the water/calcium oxide reaction is completedand all water in the blend has been scavenged; c. reacting aliphaticdiisocyanate and aromatic diisocyanate with the said resulting mixture,said aliphatic diisocyanate and said aromatic diisocyanate each havingone substantially sterically unhindered free isocyanate and onerelatively sterically hindered free isocyanate radical, said aliphaticdiisocyanate and said aromatic diisocyanate being free, except forincidental amounts, of any diisocyanate wherein both isocyanate radicalsare of substantially kinetically equal reactivity, the resulting NCO/OHratio being within the range of about 2:1 to about 3:1 and the molarratio of aromatic diisocyanate to aliphatic diisocyanate being at least1:1 but less than 7:1; and d. packaging the resulting product insubstantially hermetically sealed containers within 5 hours after thebeginning of step (c).
 13. A PROCESS ACCORDING TO CLAIM 12 WHEREIN SAIDMOISTURECURABLE POLYURETHANE COMPOSITION HAS VISCOSITY LESS THAN 800,000CENTIPOISE AT 25*C.
 14. A process according to claim 13 wherein saidmoisture-curable polyurethane composition is a paste-like sealant. 15.In a process for making a moisture-reactive composition comprising amoisture-reactive isocyanate-terminated prepolymer, which processincludes the step of utilizing an alkaline earth metal oxide as adessicant for at least one of the isocyanate-reactive starting materialsfor making said isocyanate-terminated prepolymer; said startingmaterials including a polyoxyalkylene polyol composition having anequivalent weight greater than 1000 and an average functionality greaterthan 2; the improvement which comprises: a. exothermically reactingaliphatic polyisocyanate with said polyoxyalkylene polyol composition,said aliphatic polyisocyanate being free, except for incidental amounts,of any aliphatic polyisocyanate having at least two free isocyanateradicals on the same molecule which are substantially kinetically equalto each other in their reactivity with respect to active hydrogen; b.after at least 25% of the number of equivalents of said aliphaticpolyisocyanate have reacted with said polyoxyalkylene polyolcomposition, exothermically reacting unrEacted active hydrogen in saidpolyoxyalkylene polyol composition with aromatic polyisocyanate, saidaromatic polyisocyanate being free, except for incidental amounts, ofany aromatic polyisocyanate having at least two free isocyanate radicalson the same molecule which are substantially kinetically equal to eachother in their reactivity with respect to active hydrogen, the amountsof polyisocyanate being controlled such that the ratio of aromatic NCOequivalents to aliphatic NCO equivalents reacted with saidisocyanate-reactive composition is at least about 1:1 but less than 7;1and the NCO/OH ratio for the entire moisture curable composition isgreater than about 1.8:1 but no more than about 3:1; whereby amoisture-reactive isocyanate terminted polyurethane prepolymercomposition having an average NCO functionality greater than 1.8 butless than 3.0 is obtained as a result of steps (a) and (b) and wherebythe yield of single-unit, polyurethane prepolymer in said polyurethaneprepolymer composition is maximized, said prepolymer composition, uponthe addition of a curing catalyst for the isocyanate/water reaction,being a one-part system which is curable under normal ambient conditionsto a solid which, in the form of a sheet-like article, has a tensilestrength at break greater than 25 psi.